Lenses of rotationally symmetrical configuration for distance sensors are known, portions of the round projection surface being omitted in order to adapt the lens to a predefined housing geometry. The cross-sectional shapes of the lenses are aplanar, planoconvex, biconvex, or meniscus, in each case with or without fresnel patterning; and plano-plano in the case of phase-delayed lenses with fresnel rings. These lenses have in common the fact that for a predefined distance between the so-called patches used as the transmission and reception antennas, as the horizontal lens diameter becomes smaller, the horizontal lobe angle increases but the antenna gain and thus the range of the distance sensor decreases. A specific lobe width is necessary, however, in order to sense objects located obliquely in front of the vehicle.
Three horizontally offset lobes are often used in these conventional distance sensors, for which purpose three patches are provided. The central one of the three patches lies on the longitudinal axis at the lens focal point, and the other patches horizontally to the left and right thereof. This results in three antenna lobes, one normal lobe and two diametrically "cross-eyed" lobes, which each cover a certain angular range and can be utilized for distance and angle detection of a target. Care must be taken to avoid the occurrence of zones with insufficient range between the lobes of the individual patches, so that targets located in those zones are detected too late or not at all.
As already mentioned, however, the width of the lens cannot be made as small as desired in order to enlarge the lobe angle, since otherwise the overall range becomes too small. For the case of installation in a vehicle, moreover, a lens in the shape of a horizontal rectangle is desirable.